10. Molding and casting¶

Group work¶

Our local instructor Ari taught us basics about molding and casting. We learned about milling the mold and different types of mold and cast material. We also learned about the working safety, it is important to read the material data sheet before starting the work. Use always safety glasses and gloves and do your work in a place with good ventilation.

Used materials¶

OOMOO link to TB data sheet:

Cure at room temperature with negligible shrinkage. OOMOO™ 30 has a 30-minute pot life, with a six-hour cure time.
Good for making simple one- or two- piece block molds.
Use in a properly ventilated area (“room size” ventilation). Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk. Wear vinyl gloves only. Latex gloves will inhibit the cure of the rubber. Store and use material at room temperature (23°C). Storing material at warmer temperatures will also reduce the usable shelf life of unused material. These products have a limited shelf life and should be used as soon as possible. Stir Parts A and B thoroughly before using.
Safety: Keep Out of Reach of Children. Be careful. Use only with adequate ventilation. Contact with skin and eyes may cause irritation. Flush eyes with water for 15 minutes and seek immediate medical attention. Remove from skin with waterless hand cleaner followed by soap and water.

Safety precautions for OOMOO, link to safety data sheet:

Precautions for safe handling: Use good general housekeeping procedures. Wash hands after use
Respiratory Protection: Should a respirator be needed, follow OSHA respirator regulations 29 CFR 1910.134 and European Standards EN 141, 143 and 371; wear an MSHA/NIOSH or European Standards EN 141, 143 and 371 approved respirators equipped with organic vapor cartridges.
Hand Protection: Wear any liquid-tight gloves such as butyl rubber, neoprene or PVC.
Eye Protection: Safety glasses with side shields per OSHA eye- and face-protection regulations 29 CFR 1910.133 and European Standard EN166.
Other Protective Clothing/Equipment: Additional protective clothing or equipment is not normally required.

Smooth-Sil 940 link to TB data sheet

Silicones cure at room temperature with negligible shrinkage. It is suitable for making production molds of any configuration, large or small. These silicones exhibit good chemical, abrasion and heat resistance. Materials such as plasters, concrete, wax, low-melt metal alloys or resins (urethane, epoxy or polyester) can then be cast into these silicone rubbers without a release agent.
Pot life 30 min, cure time 24 h
Mix ratio 100A:10B by weight
Safety: Be careful. Use only with adequate ventilation. Contact with skin and eyes may cause irritation. Flush eyes with water for 15 minutes and seek immediate medical attention. Remove from skin with waterless hand cleaner followed by soap and water.

Safety precautions for Smooth-Sil 940, link to safety data sheet:

Handling Precautions: Minimize breathing of vapors and avoid prolonged or repeated contact with skin. Wear proper protective equipment.
Ventilation: Provide general or local exhaust ventilation systems
Protective Clothing/Equipment: Wear chemically protective gloves. Wear protective eyeglasses per OSHA eye and face protection regulations

Smooth-Cast® 300 link to TB data sheet

The Smooth-Cast™ 300 Series of liquid plastics are ultra-low viscosity casting resins that yield castings that are bright white and virtually bubble free. Vacuum degassing is not necessary. They offer the convenience of a 1A:1B by volume or 100A:90B by weight mix ratio. The differences between them are pot life and demold time.
Pot life 3 min, cure time 10 min.
Safety - Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk. Use only in a well-ventilated area
Preparation - These products have a limited shelf life and should be used as soon as possible. Materials should be stored and used in a warm environment (23°C). All liquid urethanes will react with moisture in the air, causing bubbles. Use in a low humidity environment (below 50% RH). Mixing containers should have straight sides and a flat bottom. Mixing sticks should be flat and stiff with defined edges for scraping the sides and bottom of your mixing container.

Safety precautions for Smooth-Cast 300, link to safety data sheet:

Handling Precautions: Minimize breathing of vapors and avoid prolonged or repeated contact with skin. Wear proper protective equipment. If ventilation is not sufficient, wear proper respiratory equipment. Avoid moisture contamination.
Respiratory Protection: Follow OSHA respirator regulations 29 CFR 1910.134 and European Standard EN 149; wear an MSHA/NIOSH or European Standard EN149 approved respirator.
Protective Clothing/Equipment: Wear chemically protective gloves. Wear protective eyeglasses per OSHA eye and face protection regulations

Regarding respiratory Protection regulation, it mainly says (from OSHA respirator regulations 29 CFR 1910.134 ) ” shall be accomplished as far as feasible by accepted engineering control measures (for example, enclosure or confinement of the operation, general and local ventilation, and substitution of less toxic materials) ” and ” A respirator shall be provided to each employee when such equipment is necessary.”

Molding and casting¶

Our group: Perttu, Gleb, Lucasz and I.

We used the molds made last year to test materials. We used gloves, safety glasses and lab coats.

We started with OOMOO. We first read the data sheet to see the user instructions and mixing rate.

We mixed the parts thoroughly and measured the parts by weight: 100A:130B

We stirred the mixture well

and put it in vacuum to remove air from the mixture

We poured the mixture in the mold and flattened the surface.

Next we used Smooth-Sil 940 that has mixture ratio of parts: 100A:10B

We stirred and vacuumed the mixture

and poured it in the mold.

Next we tried casting polyurethane with two part mold and one part mold

and polyurethane was used also to cast this two part mold

We left all the molds to cure

After curing time we demolded the silicons and polyurethanes with injected air.

Results look very nice.

Comparison of Materials

Smooth Cast 300

A:B Mix Ratio by Volume: 1A:1B
A:B Mix Ratio by Weight: 100A:90B
Pot Life: 3 min
Cure Time: 10 min

OOMOO™ 30 Silicone Rubber

A:B Mix Ratio by Volume: 1A:1B
A:B Mix Ratio by Weight: 100A:130B
Pot Life: 30 min
Cure Time: 6 hours

Smooth-Sil™ 940

A:B Mix Ratio by Volume: 100A:10B
A:B Mix Ratio by Weight: 100A:10B
Pot Life: 30 min
Cure Time: 24 hours

Metal casting¶

Our local instructor Ari show us also how to cast metal. The material is tin-antimony mixture and the melting point is around 240 Celsius.

Individual assignment¶

Design¶

I designed a diamond shape using Fusion 360.

I started the diamond design by drawing a Circumscribed Polygon with 16 edges and extruded it to 5 mm thickness. After that I extruded again 5 mm with -35 degree Taper Angle.

Then I draw a construction plane and used Modify / Split Body tool to cut the edge.

After that I used Pattern tool to copy the feature arounf the diamond.

I repeated this procuedure with different extrusion thicknesses and angles.

After the diamond was ready I cut it in two halves.

After that I created circular boxes around the halves by drawing a circle and extruding it to the needed hight (25 mm). I added also holes for injection and air by drawing and extruding rectangulars with rounded fillets to the other half of the diamond.

I saved the design as stl file.

When I was about to start the milling I noticed that the design is too big for the wax brick that is available. I needed to scale down the size. That is easy by using Fusion 360 Modify / Scale -tool. I reduced the size to 0.7.

With the new stl file I started the milling.

I used tape in the bottom of the wax brick for attaching it to the milling bed. I was difficult to get it to hold to the bed, in my case the brick started to move and I had to stop the milling. This happened two times.

First I opened Roland VPanel and set the x- y- and z- origin points.

Then I opened the diamond mold.stl file with MODELA Player 4 tool to set the milling routes.

First I chose Set/Model and I set the orientation and origin. My design seemed to be upside down, so I turned it. I also chose the origin

I used 3.18 mm flat milling bit with two flutes for both roughing and finishing.

Next I started a new process by choosing Set/New process and choosing “Roughing” .

Toolpath contour lines are ok with Up Cut

Modelling Wax parameters are ok

XY Speed: 30 mm/sec
Z Speed: 10 mm/sec
Spindle: 7000 rpm
Cutting-in Amount: 1 mm
Path Interval: 1.5 mm
Finish Margin: 0,2 mm

Now the program shows the toolpaths based on the settings.

Next I created the finishing process with New Process, this is done in the same way as the Roughing process.

I chose X+Y Scanlines for the type of toolpath so that the surface would be smooth.

Cutting position set up was ok.

For Finishing the Modelling Wax parameters are

XY Speed: 19,49 mm/sec
Z Speed: 19,49 mm/sec
Spindle: 7000 rpm
Cutting-in Amount: 0,2 mm
Path Interval: 0,2 mm
Finish Margin: 0 mm

I opened File -> Preview Cutting to see the simulation of the cutting.

Now everything was ready for the milling so I press the start button in the right lower corner

and the milling started when pressing Continue

When the milling was done (Roughing and Finishing) I removed the wax brick from the milling chamber and cleaned the machine with brush. The wax crumbs will be re-used by melting them into new bricks.

Here is the milled mold. It is ok, there are some stripes that are not in the design though. It is possible that they are caused by the small movement of the brick (the tape attachment was not holding properly).

I did not have the mold surrounding filled in my design and MODELA Player 4 mills also the outside of the mold. This is needless operation and just adds milling time, so next time I sure will design the filled surrounding.

I used Smooth-Sil 940 for silicone mold casting

I mixed the parts, vacuumed the mixture and poured the mixture in the molds.

Next day I demolded the silicon mold, it looks very nice.

Then I prepared the needed materials for the actual casting. I used Smooth-Cast 310

I mixed the parts and used syringe to inject the mixture in the mold. Syringe is needed because the hole for the material is so small.

I used tape to hold the mold parts together.

After four hours curing I demolded my diamond.

The mold had fallen down and small amount of mixture had come out. This is why there is a big air bubble in the other side. Otherwise the diamond looks good.

Reflection¶

Molding and casting was completely new to me. It was very nice to see and learn how molds are created. Especially I did not know the positive/negative mold concept earlier.

It was also nice to see how various materials can be used.

Milling the wax mold is quite slow and I didn’t realize that early enough, any extra milling for mold surrounding should be left out in the design. I had problems to attach the wax brick to milling machine bed properly and that took a lot of extra time.

Files¶

Mold Fusion f3d file
Mold stl file
Mold mpj file created by MODELA 4 Player for the milling